Heat Exchanger Design and Selection

Understanding Heat Exchangers: The Foundation of Thermal Management

Heat exchangers represent one of the most critical components in industrial processes, HVAC systems, and manufacturing facilities across Atlantic Canada. These devices, which transfer thermal energy between two or more fluids at different temperatures, are essential for everything from seafood processing plants along Nova Scotia's coastline to pulp and paper mills throughout the Maritimes. Understanding the principles of heat exchanger design and selection is crucial for engineers, facility managers, and operations personnel who must balance efficiency, cost, and reliability in their thermal management systems.

In the challenging climate of Nova Scotia and the broader Maritime region, where temperatures can swing from -25°C in winter to +30°C in summer, properly designed heat exchangers become even more critical. Whether you're recovering waste heat from industrial processes, conditioning air for commercial buildings in Halifax, or maintaining optimal temperatures in food processing facilities in Amherst, the right heat exchanger selection can dramatically impact both operational efficiency and bottom-line costs.

Types of Heat Exchangers and Their Applications

Selecting the appropriate heat exchanger type is the first critical decision in any thermal system design. Each configuration offers distinct advantages depending on the application, available space, fluid properties, and performance requirements.

Shell and Tube Heat Exchangers

Shell and tube heat exchangers remain the most widely used type in industrial applications, accounting for approximately 35-40% of all heat exchangers in service globally. These robust units consist of a bundle of tubes enclosed within a cylindrical shell. One fluid flows through the tubes while the other flows over them within the shell.

• Operating pressures: Can handle pressures exceeding 1,000 bar in specialised applications

• Temperature range: Suitable for temperatures from -200°C to over 600°C

• Heat transfer area: Available in sizes from 1 m² to over 10,000 m²

• Typical applications: Oil refineries, power plants, chemical processing, marine systems

For Maritime industries such as offshore oil and gas support services and marine vessel operations, shell and tube exchangers offer the durability and reliability essential for harsh operating environments.

Plate Heat Exchangers

Plate heat exchangers utilise thin, corrugated metal plates to transfer heat between fluids. Their compact design and high thermal efficiency make them increasingly popular in applications where space is limited or where frequent cleaning is required.

• Heat transfer coefficients: Typically 3-5 times higher than shell and tube designs

• Footprint: Up to 80% smaller than equivalent shell and tube units

• Plate materials: Stainless steel 304/316, titanium, Hastelloy, nickel alloys

• Typical applications: HVAC systems, food and beverage processing, pharmaceutical manufacturing

Nova Scotia's thriving seafood processing industry frequently employs plate heat exchangers for pasteurisation, cooling, and heat recovery applications, where sanitary design and ease of cleaning are paramount.

Air-Cooled Heat Exchangers

Also known as fin-fan coolers, air-cooled heat exchangers use ambient air as the cooling medium, eliminating the need for cooling water. These units are particularly valuable in locations where water is scarce or expensive to treat.

Double-Pipe Heat Exchangers

The simplest heat exchanger configuration, double-pipe units consist of one pipe placed concentrically inside another. While limited in capacity, they offer advantages for high-pressure applications and situations requiring true countercurrent flow.

Key Design Parameters and Calculations

Effective heat exchanger design requires careful consideration of multiple thermal and hydraulic parameters. Understanding these fundamentals enables engineers to optimise performance while minimising capital and operating costs.

Heat Transfer Fundamentals

The basic heat transfer equation governs all heat exchanger designs:

Q = U × A × ΔTLM

Where Q represents the heat duty (kW), U is the overall heat transfer coefficient (W/m²·K), A is the heat transfer area (m²), and ΔTLM is the log mean temperature difference (K).

For typical industrial applications in Atlantic Canada, overall heat transfer coefficients range from:

• Water to water: 850-1,700 W/m²·K

• Water to oil: 110-350 W/m²·K

• Steam to water: 1,000-4,000 W/m²·K

• Air to water (finned): 25-50 W/m²·K

Pressure Drop Considerations

Pressure drop through a heat exchanger directly impacts pumping costs and system performance. Design engineers must balance the benefits of higher fluid velocities (improved heat transfer) against increased pressure losses. For most liquid applications, pressure drops between 35-70 kPa represent an acceptable compromise. Gas-side pressure drops are typically limited to 1-5% of the absolute operating pressure.

Fouling Factors

Fouling—the accumulation of deposits on heat transfer surfaces—significantly impacts long-term performance. The TEMA (Tubular Exchanger Manufacturers Association) standards provide recommended fouling factors for various services:

• Clean river water: 0.00035 m²·K/W

• Seawater (coastal Nova Scotia): 0.00009-0.00035 m²·K/W

• Fuel oil: 0.00088 m²·K/W

• Refrigerants: 0.00018 m²·K/W

For facilities using seawater from the Bay of Fundy or Northumberland Strait, fouling considerations become particularly important due to the high biological activity in Maritime waters.

Material Selection for Maritime Environments

The selection of appropriate materials is crucial for heat exchanger longevity and performance, particularly in Atlantic Canada's challenging coastal environment where corrosion and environmental factors demand careful consideration.

Corrosion Resistance

Maritime facilities face unique corrosion challenges from salt-laden air, brackish water, and seawater cooling. Common material choices include:

• 316L Stainless Steel: Excellent general corrosion resistance; suitable for most freshwater and mild chemical applications

• Titanium Grade 2: Outstanding seawater resistance; increasingly cost-competitive for coastal installations

• Copper-Nickel Alloys (90/10, 70/30): Traditional choice for seawater service with good biofouling resistance

• Duplex Stainless Steels: Superior strength and corrosion resistance for demanding applications

Temperature and Pressure Ratings

Material selection must account for both design and upset conditions. Canadian Standards Association (CSA) and ASME codes govern pressure vessel design, requiring appropriate safety factors. For Nova Scotia installations, materials must also withstand the thermal cycling inherent in our climate, with outdoor equipment potentially experiencing temperature variations of 50°C or more throughout the year.

Energy Efficiency and Heat Recovery

With rising energy costs and increasing environmental regulations, heat recovery has become a priority for industrial facilities across the Maritimes. Well-designed heat exchanger systems can recover 60-90% of waste heat, delivering significant economic and environmental benefits.

Waste Heat Recovery Applications

Common heat recovery opportunities in Atlantic Canadian industries include:

• Boiler flue gas economisers: Recovering heat from stack gases to preheat feedwater, improving boiler efficiency by 4-8%

• Compressor heat recovery: Capturing heat from compressed air systems for space heating or process use

• Process cooling water: Using warm cooling water for building heating during Nova Scotia's long winter months

• Refrigeration condenser heat: Recovering heat from refrigeration systems in food processing plants

Payback Analysis

For a typical Nova Scotia manufacturing facility spending $500,000 annually on heating fuel, installing heat recovery exchangers with 70% efficiency can generate savings of $175,000-$250,000 per year. With capital costs for heat recovery systems typically ranging from $50,000-$300,000 depending on scale and complexity, payback periods of 1-3 years are commonly achievable.

Installation, Commissioning, and Maintenance Best Practices

Even the best-designed heat exchanger will underperform if improperly installed or maintained. Following established best practices ensures optimal performance throughout the equipment's service life.

Installation Considerations

• Foundation design: Adequate structural support accounting for equipment weight, thermal expansion, and vibration

• Piping flexibility: Proper expansion loops or joints to accommodate thermal movement

• Accessibility: Sufficient clearance for tube bundle removal, plate pack inspection, or shell access

• Instrumentation: Temperature, pressure, and flow measurement for performance monitoring

Commissioning Procedures

Proper commissioning includes hydrostatic testing per applicable codes (typically 1.3-1.5 times design pressure), leak testing of all connections, verification of instrument calibration, and baseline performance documentation. This baseline data becomes invaluable for tracking performance degradation over time.

Preventive Maintenance

Regular maintenance activities should include:

• Monthly: Log operating parameters; compare against baseline performance

• Quarterly: Inspect gaskets and seals; check for external corrosion

• Annually: Conduct detailed performance analysis; plan cleaning if efficiency has dropped more than 10-15%

• Every 3-5 years: Internal inspection; thickness measurements; gasket replacement for plate exchangers

Regulatory Compliance and Canadian Standards

Heat exchanger installations in Nova Scotia must comply with various federal, provincial, and industry codes and standards. Key regulatory considerations include:

• CSA B51: Boiler, Pressure Vessel, and Pressure Piping Code—governing registration and inspection requirements

• ASME Section VIII: Rules for Construction of Pressure Vessels—the primary design code for most heat exchangers

• TEMA Standards: Tubular Exchanger Manufacturers Association guidelines for shell and tube exchangers

• Nova Scotia Technical Safety Act: Provincial requirements for pressure equipment registration and periodic inspection

Working with registered Professional Engineers ensures that heat exchanger designs meet all applicable codes and can be successfully registered with provincial authorities. This is particularly important for equipment operating above threshold pressures or containing hazardous materials.

Partner with Sangster Engineering Ltd. for Your Heat Exchanger Projects

Designing, selecting, and implementing heat exchanger systems requires expertise across multiple engineering disciplines—thermodynamics, fluid mechanics, materials science, and process engineering. At Sangster Engineering Ltd., our team of Professional Engineers brings decades of combined experience in mechanical system design for industrial, commercial, and institutional clients throughout Nova Scotia and Atlantic Canada.

From initial feasibility studies and heat balance calculations through detailed design, equipment specification, and construction support, we provide comprehensive engineering services tailored to your specific requirements. Our familiarity with local conditions, Maritime industries, and Canadian regulatory requirements ensures that your heat exchanger installation will deliver reliable, efficient performance for years to come.

Contact Sangster Engineering Ltd. today to discuss your heat exchanger design and selection needs. Whether you're upgrading existing equipment, designing a new facility, or exploring heat recovery opportunities to reduce your energy costs, our Amherst-based team is ready to help you achieve your thermal management objectives.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.